Power bank



FIG. 1 is a top, front and right side perspective view of a power bank, showing my new design;

FIG. 2 is a bottom, rear and left side perspective view;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines in the drawings illustrate the portions of the power bank, which form no part of the claimed design. 

CLAIM The ornamental design for a power bank, substantially as shown and described. 